This is at https://github.com/netwide-assembler/nasm/blob/3aebb20f123033dcd767f0abc46b18cbefed8091/asm/preproc.c#L1842

$ git diff
diff --git a/asm/preproc.c b/asm/preproc.c
index 0ff2b518..fb64b6b8 100644
--- a/asm/preproc.c
+++ b/asm/preproc.c
@@ -1841,7 +1841,7 @@ static Token *new_Token_free(Token * next, enum token_type ty
pe,

     if (txtlen <= INLINE_TEXT) {
         memcpy(t->text.a, text, txtlen);
-        free(text);
+        nasm_free(text);
     } else {
         t->text.p.ptr = text;
     }